Let's move onto another story now. America is politically polarized, which means whenever someone is nominated to be a judge, the first question that gets asked is whether the nominee is liberal or conservative. We've heard this question many times, but political preferences are not the only sources of influence on judicial decisions. New research finds that the children of judges may play a surprisingly important role. NPR's Shankar Vedantam joins us each week on this program to talk about social science research, and he spoke with my colleague, Steve Inskeep, about this study.

STEVE INSKEEP, HOST:

So what's happening here, the kids are telling the judges how to rule?

SHANKAR VEDANTAM, BYLINE: Not quite, Steve. This research is looking at how the life experiences of judges might affect how they rule from the bench. Now this is a surprisingly difficult question to study empirically, because you can't conduct controlled experiments on judges. You can't change their race or gender or political affiliation, and see how that changes their rulings.

INSKEEP: Oh, yeah, OK.

VEDANTAM: So I was speaking with Maya Sen, she is a political scientist at the University or Rochester, and along with Adam Glynn, at Harvard, she realized that mother nature was actually conducting a randomized experiment on judges when it came to one factor, the gender of their kids.

MAYA SEN: Once a couple decides to have a child, then essentially what happens is that nature comes in and does a version of a coin toss. And if it comes up heads, then the couple will have a girl, and if it comes up tails, the couple will have a boy, and so essentially the gender of the child is outside of the couple's control.

INSKEEP: Okay so they're wondering what factors influence a judge's decision besides the cold objectivity of the law. They get wondering if parenting affects your decisions and they're able to check before and after these parents have kids.

VEDANTAM: Exactly, they wanted to factor that the judges themselves didn't have control over, and the gender of their kids is not a factor that the judges had control over. So Sen and Glynn studied 2600 rulings of 240 judges on the US Court of Appeals and they looked to see if having a daughter made a difference to their rulings. Now there's lots of anecdotal evidence that personal experiences of judges make a difference. On the Supreme Court for example Harry Blackman, who wrote the famous Roe v. Wade opinion - apparently he had a teenage daughter who got pregnant and there's been some speculation that that informed his writing in Roe v. Wade.

INSKEEP: Makes sense.

VEDANTAM: Justice John Paul Stevens, a World War II veteran, you know, he was usually a strong proponent of first amendment, freedom of speech issues, but when it came to flag burning, he sort of drew the line and I think his military experience may have informed his position on that. So, what Sen and Glynn wanted to find out is whether there was empirical evidence that judges could be influenced in this way, and specifically whether having daughters change the way judges ruled. Here's Sen.

SEN: We found having at least one daughter means that a judge will be about 7 percentage points more likely to vote in sort of a feminist direction on gender related cases. Things like employment discrimination, pregnancy discrimination, abortion, Title IX, things like this.

INSKEEP: Seven percent more likely to vote in a feminist direction. How significant is that?

VEDANTAM: Well, It doesn't seem like very much, but Sen explained to me that if you think about the ideological difference between judges who are republicans and judges who are democrats, seven percentage points is about half that partisan difference, so it's actually a sizable amount. Now interestingly they find that this effect is strongest among republican men. So, male republican judges with daughters are most likely to vote differently than male republican judges who don't have daughters. And also this difference emerges only for cases involving gender. It doesn't emerge for cases involving bankruptcy or other kinds of the law.

INSKEEP: So what do we think is happening here, that you have a judge who has this personal experience with having a daughter which causes them to be exposed to different points of view or think about women and girls in a different way?

VEDANTAM: Well, that seems to be the argument that Sen and Glynn are making. You could make the argument that judges with daughters are being biased, but you could just as easily make the argument that compared to judges who have daughters, judges who have sons are biased in a different direction. And I think what the study is pointing to is the fallacy of imagining that judges rule on the bench without bringing their personal experiences to bear. The better question to ask might be, what biases do you want the judges to have, not whether the judges are biased at all.

INSKEEP: What do you mean, what biases do you want the judges to have?

VEDANTAM: Well, what life experiences do you want to see represented on the bench because the life experiences of the judges seem to affect how they rule, and if those life experiences don't match the people who are being judged, there's going to be a mismatch between what happens with the bench and who's appearing before the bench.